Environment
Generating electricity using glass production exhaust gas Matthias Hagen* and Sven Jensen** explore the obstacles and opportunities of using excess heat from flue gases to aide improve sustainable glass manufacturing.
M
Exhaust gas volume flow
Recoverable electricity
30.000 Nm³/h
250 to 420 kW
45.000 Nm³/h
375 to 630 kW
60.000 Nm³/h
500 to 840 kW
� Fig 2. Recoverable electric energy depending on
� Fig 1. Chart of the heat recovery over air volume.
can be extracted and transferred to warm water or thermal fluid. But many glass factories do not have a direct use for it. The own requirement for hot water is small and in rare cases it is possible to feed into a district heating
2
Evaporator Heat transfer from heat source to working media
3
Turbogenerator Thermal power is partially converted into electric power
network nearby. The ideal solution is the conversion of thermal energy into electric power. This is possible with an Organic Rankine Cycle Continued>>
4
Power generation Electric power feed line to the grid
5
Condenser Condensation of working media vapor
1
6
Heat supply Heat transfer medium flows from the heat source into the ORC Module
Heat extraction Condensation heat, that can be utilised for follow-up processes
7 Pump Recirculation of the working media
� Fig 3. Principles of the ORC technology.
the volume flow.
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ajor glass companies are currently looking for possibilities to reduce CO2 emissions. As glass production is an energy intensive process, the main target is to reduce or replace the use of fossil fuels. Kiln suppliers are shifting from fossil to electric firing and the use of hydrogen is an ongoing discussion. Regardless of the type of fuel used in the kiln, all furnaces will create flue gases with temperatures between 280 °C and 550 °C. This temperature range depends on the installed heat recovery with recuperators or in most cases regenerators. Experience shows that the composition of the flue gases and the dust content poses a constant threat to the equipment. Internals of the regenerators, refractory parts called checkers, will clog and so the recovery of heat will be reduced. Although periodical thermal cleaning helps to reduce deposits manual cleaning is required in the long term. This illustrates the difficulties in handling dust containing flue gases. However, the exhaust gases represent a huge potential for energy recovery. In most cases it is not utilised today (Fig.1). Typically, the thermal energy is dissipated to ambient due to cooling requirements for the flue gas treatment with a bag filter and sent to the atmosphere through the stack. By installing a heat exchanger in the flue gas flow, valuable thermal energy
43 Glass International July/August 2021
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